In conditions of a competitive and turbulent business environment, the importance of human resources for the modern organization is increasingly emphasized. Human resources become the most important organizational resource that allows the survival, growth and development of organizations participating in market competition. Since people are the only living element common to all organizations, differentiation of successful from unsuccessful organizations will largely depend on the management of human resources. Namely, only high-quality human resource management will ensure the achievement of organizational objectives and contribute to organizational success. In that context, a permanent challenge and task of human resources management is filling positions in the organization, retaining and motivating the best employees and continuous education, training and staff development. However, given that the execution of tasks and duties within the job description of an employee in modern business conditions is no longer sufficient to meet the goals of the organization and its success, there is a need for the employee's behavior that goes beyond the formal terms of job description, in other words organizational citizenship behavior. Therefore, the term organizational citizenship behavior implies individual discretionary behavior that is not directly or explicitly recognized by the formal reward system, and which supports efficient and effective functioning of the organization. In addition to the theoretical part, the thesis consists of empirical research by which employees’ perceptions about their organizational citizenship behavior are explored. Survey of employee perception in one large Croatian company on their own organizational citizenship behavior showed that participants in the study have a high degree of perception in terms of their own practice of organizational citizenship behavior with the highest average degree of agreement with statements regarding the dimension of altruism.